In oilfield operations, elevators are generally employed to connect a tubular to a hoist, enabling the tubular to be lifted into place, made up to a string of tubulars, and run into a wellbore. One type of elevator is a side-door elevator, which latches onto the tubular and engages the box threaded coupling at one end of the tubular. The other end of the tubular includes a pin threaded coupling, which is received and threaded into the box threaded coupling of the previously-run tubular. Once connected (“made-up”) to the rest of the string of tubulars, the string weight is supported by connection between the elevator and the tubular at the threaded coupling.
Another type of elevator is a slip-type elevator, sometimes refereed to as a “YC” elevator. The slip-type elevator includes slips, which may have teeth or be non-marking, that engage the outer diameter of the tubular. Typically, the slips are pushed radially inward into engagement with the outer diameter of the tubular. The radial force is provided by an axial engagement between a setting plate and an upset or shoulder, generally at the end of the shoulder. Using a tapered interface, the axial engagement of the setting plate with the upset is translated into radially-inward force on the slips, causing the slips to engage the tubular. Thus, once made up to the tubular string, the weight of the string is supported by the outer diameter of the tubular, rather than the threaded connection.
However, some tubulars employ an integral swaged or tapered box at the end of the tubular to accommodate the pin of the next tubular. Such integral, swaged box designs incorporate a gradual increase in the inner and outer diameter of the tubular to accommodate the interior threads, allowing the tubular to be made up to the pin connection of the next tubular.
To transfer this type of tubular from a horizontal position (i.e., as stored on the surface) to a vertical position (for being made-up and run in), a threaded insert, referred to as a “lift nubbin” is threaded into the swaged box. The lift nubbin has a larger outer diameter at the top, which serves as the upset. However, this design requires the use of a special bored side door to correctly interface with the shoulder of the lift nubbin, due to the larger outer diameter of the swaged box. Further, slip-type elevators are generally not acceptable for use with the swaged box tubulars, because the taper of the swaged box may cause the slips of the elevator to engage the tapered region of swaged box, resulting in an incomplete engagement of the outer diameter of the tubular. This, in turn, can result in increased local stress in the areas where the slips engage.